Diol derivatives such as α-hydroxycarboxylic acid esters, α-hydroxycarboxylic acids, and polyglycolic acid are widely used as starting materials for various industrial products and so on.
For example, α-hydroxycarboxylic acids are compounds that are industrially important as, for example, polymerization monomers used as starting materials for various synthetic resins. Conventionally, α-hydroxycarboxylic acid esters are produced through esterification by reacting an α-hydroxycarboxylic acid and an alcohol together.
However, industrial grade α-hydroxycarboxylic acids are aqueous solutions and have low purity, and hence it is difficult to obtain high-purity α-hydroxycarboxylic acid esters using the conventional method. Moreover, in the case of using a high-purity α-hydroxycarboxylic acid, the starting material is expensive, and hence an α-hydroxycarboxylic acid ester cannot be obtained economically.
α-hydroxycarboxylic acids are compounds that are industrially important as, for example, polymerization monomers used as starting materials for various synthetic resins such as polyglycolic acid. In particular, glycolic acid is used, for example, as a metal cleaning agent for cleaning printed circuit boards and the like, and a scale inhibitor for boilers and so on. In addition, in recent years glycolic acid has come to be used as a base cosmetic, a cosmetic liquid or the like having an anti-wrinkle effect.
Conventionally, glycolic acid is predominantly produced using (1) a method in which carbon monoxide, formaldehyde and water are reacted together at high pressure with acid catalysis, or (2) a method in which chloroacetic acid and sodium hydroxide are reacted together. Glycolic acid produced using these methods contains as impurities, for example, formaldehyde, chlorine-containing compounds, organic acids other than glycolic acid such as methoxyacetic acid, and so on.
As glycolic acid for use in cosmetics and so on, there are thus calls for high-purity glycolic acid not containing such impurities.
However, it is difficult to isolate and purify glycolic acid using commonly used purification methods such as distillation, and in particular it is difficult to completely remove impurities such as the above. In actual practice, high-purity glycolic acid obtained by removing the impurities as much as possible from industrial grade glycolic acid containing large amounts of impurities is used.
Industrial grade glycolic acid that is commercially available is predominantly produced using the following two methods. The first method is a carbonylation reaction of folmaldehyde with carbon monoxide high temperature and high pressure in the presence of an acid catalyst. The industrial grade glycolic acid obtained using this production method takes the form of a 70% aqueous solution, and contains a total more than 10 wt % relative to the glycolic acid of glycolic acid dimer, diglycolic acid, methoxyacetic acid, formic acid and so on as organic acids other than glycolic acid. These impurities cannot be separated off using a method such as distillation. A complex purification process must thus be passed through, and moreover there is a problem that the yield is low.
Moreover, although high-purity glycolic acid obtained using this production method is commercially available, the price of such glycolic acid having a purity of 99% or more is high, being more than 10 times that of industrial grade glycolic acid, and hence widespread uses are limited.
The other method of producing glycolic acid is a method in which monochloroacetic acid is hydrolyzed using sodium hydroxide and then neutralization is carried out. With this method, double the stoichiometric amount of sodium hydroxide is consumed as an auxiliary starting material, and hence there is a problem that a large amount of sodium chloride contaminated with organic compound is generated as waste.
There are thus strong calls for the development of a method enabling high-purity glycolic acid not containing impurities such as formaldehyde and chlorine-containing compounds to be produced economically.
Methods of producing polyglycolic acid can be broadly classified into the following two methods. One is a method in which glycolic acid or a glycolic acid ester is subjected to polycondensation directly. The other is a method in which glycolide, which is acyclic dimer of glycolic acid is first produced, and then the glycolide is subjected to ring-opening polymerization.
To produce high-molecular-weight polyglycolic acid using such a method, it is necessary to precisely control the purity of the glycolic acid or glycolic acid ester used as the starting material and the types and amounts of impurities. For example, it is thought that impurities such as methoxyacetic acid esters and diglycolic acid ester inhibit polymerization, and hence it is preferable to remove these impurities as much as possible.
Generally commercially available industrial grade glycolic acid is a 70% aqueous solution. This contains a total of more than 10 wt % relative to the glycolic acid of glycolic acid dimer, diglycolic acid, methoxyacetic acid, formic acid and so on as organic acids other than glycolic acid. To obtain high-quality high-molecular-weight polyglycolic acid, it is essential to use a purified glycolic acid ester as the starting material. Consequently, to produce a high-purity glycolic acid ester from industrial grade glycolic acid, it is necessary to pass through a large number of steps such as recrystallization of the glycolic acid, oligomerization, alcoholysis, and distillation (International Patent Publication No. WO99/19378).
Moreover, high-purity glycolic acid having a purity of 99% or more has also been produced (U.S. Pat. No. 3,859,349). However, the price thereof is high, being more than 10 times that of industrial grade glycolic acid. It is thus not possible to provide polyglycolic acid inexpensively.
In the case of the method of producing polyglycolic acid via glycolide, again complex operations are required for producing and purifying the glycolide. Moreover, regarding the purification of the glycolic acid that is a starting material of the glycolide or the glycolic acid or glycolic acid ester that is a starting material of the polyglycolic acid, as above it is necessary to pass through a large number of steps, and hence the purification is very costly (International Patent Publication No. WO01/72736).
In this way, it is difficult to produce high-molecular-weight high-quality polyglycolic acid economically regardless of which method is used. Moreover, there are also calls for the development of a method of producing high-quality glycolic acid esters inexpensively.
It is thus a principal object of the present invention to produce high-purity diol derivatives at lower cost.